Interstellar matter in early-type galaxies. II - The relationship between gaseous components and galaxy types

Bregman, Joel N.; Hogg, D. E.; Roberts, M. S.

doi:10.1086/171101

Cited by 108 publications

(135 citation statements)

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“…The mean R within different 'age' bins (of variable width) is also shown in the same figure. In agreement with our previous result the mean R parameter for pre-mergers, although on average higher than that of isolated spirals (≈ 0.8 dex; Young & Knezek (1989) and Bregman, Hogg & Roberts (1992) respectively. The filled circle is the ring system ESO 034-IG11.…”

Section: Radio Flux Densitysupporting

confidence: 92%

“…Elliptical galaxies are also known to have little cold gas. This is demonstrated in Figure 6 showing the mean [M (HI)+M (H2)]/LB ratio for ellipticals (Bregman, Hogg & Roberts 1992). Although merger remnants are gas rich compared to normal ellipticals, they seem to form a sequence that supports the merger scenario as a possible formation mechanism for elliptical galaxies.…”

Section: Cold Gasmentioning

confidence: 81%

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Cold gas and star formation in a merging galaxy sequence

Georgakakis

Forbes

Norris³

2000

Monthly Notices RAS

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We explore the evolution of the cold gas (molecular and neutral hydrogen) and starformation activity during galaxy interactions, using a merging galaxy sequence comprising both pre-and post-merger candidates. Data for this study come from the literature but supplemented by some new radio observations presented here. Firstly, we confirm that the ratio of far-infrared luminosity to molecular hydrogen mass (L F IR /M (H 2 ); star-formation efficiency) increases close to nuclear coalescence. After the merging of the two nuclei there is evidence that the star-formation efficiency declines again to values typical of ellipticals. This trend can be attributed to M (H 2 ) depletion due to interaction induced star-formation. However, there is significant scatter, likely to arise from differences in the interaction details (e.g. disk-to-bulge ratio, geometry) of individual systems. Secondly, we find that the central molecular hydrogen surface density, Σ H2 , increases close to the final stages of the merging of the two nuclei. Such a trend, indicating gas inflows due to gravitational instabilities during the interaction, is also predicted by numerical simulations. Furthermore, there is evidence for a decreasing fraction of cold gas mass from early interacting systems to merger remnants, attributed to neutral hydrogen conversion into other forms (e.g. stars, hot gas) and molecular hydrogen depletion due to on-going star-formation. The evolution of the total-radio to blue-band luminosity ratio, reflecting the total (disk and nucleus) star-formation activity, is also investigated. Although this ratio is on average higher than that of isolated spirals, we find a marginal increase along the merging sequence, attributed to the relative insensitivity of disk star-formation to interactions. However, a similar result is also obtained for the nuclear radio emission, although galaxy interactions are believed to significantly affect the activity (star-formation, AGN) in the central galaxy regions. Nevertheless, the nuclear-radio to blue-band luminosity ratio is significantly elevated compared to isolated spirals. Finally, we find that the FIR-radio flux ratio distribution of interacting galaxies is consistent with star-formation being the main energising source.

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Section: Radio Flux Densitysupporting

confidence: 92%

Section: Cold Gasmentioning

confidence: 81%

Cold gas and star formation in a merging galaxy sequence

Georgakakis

Forbes

Norris³

2000

Monthly Notices RAS

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“…In the past, two different research groups have built up comparison samples in order to study the variation of the gas content of galaxies along the Hubble sequence: Bregman et al (1992) and Casoli et al (1998). Bregman et al (1992) derived the content of molecular gas, HI, X-ray emitting gas and dust, working on a sample of 467 early-type galaxies, ranging from pure ellipticals (E, t = −5) to early spirals (Sa, t = 1).…”

Section: Building Up a Comparison Samplementioning

confidence: 99%

“…Bregman et al (1992) derived the content of molecular gas, HI, X-ray emitting gas and dust, working on a sample of 467 early-type galaxies, ranging from pure ellipticals (E, t = −5) to early spirals (Sa, t = 1). In their analysis they favoured the use of the total blue luminosity (L B ) of galaxies as the necessary normalisation factor, i.e., the in-…”

Section: Building Up a Comparison Samplementioning

confidence: 99%

The gas content of peculiar galaxies: Counterrotators and polar rings

Bettoni

Galletta

García‐Burillo

et al. 2001

A&A

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Abstract. This paper studies the global ISM content in a sample of 104 accreting galaxies, including counterrotators and polar rings, which spans the entire Hubble sequence. The molecular, atomic and hot gas content of accretors is compared to a newly compiled sample of normal galaxies. We present results of a small survey of the J = 1−0 line of 12 CO with the 15 m SEST telescope on a sample of 11 accretors (10 counterrotators and 1 polar ring). The SEST sample is enlarged with published data from 48 galaxies, for which observational evidence of counterrotation in the gas and/or the stars has been found. Furthermore, the available data on a sample of 46 polar ring galaxies has been compiled. In order to explore the existence of an evolutionary path linking the two families of accretors, the gas content of counterrotators and polar rings is compared. It was found that the normalized content of cold gas (Mgas/LB) in polar rings is ∼1 order of magnitude higher than the reference value derived for normal galaxies. The inferred gas masses are sufficient to stabilize polar rings through self-gravity. In contrast, it was found that the cold gas content of counterrotators is close to normal for all galaxy types. Although counterrotators and polar rings probably share a common origin, the gas masses estimated here confirm that light gas rings accreted by future counterrotators may have evolved faster than the self-gravitating structures of polar rings. In this scenario, the transformation of atomic into molecular gas could be enhanced near the transition region between the prograde and the retrograde disks, especially in late-type accretors characterized by a high content of primordial gas. This is tentatively confirmed in this work: the measured H2/HI ratio seems larger in counterrotators than in normal or polar ring galaxies for types later than S0s.

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“…The hot gas component dominates the ISM in E/S0 galaxies, and only comparatively small quantities are detected in the warm and cold phases (Bregman et al 1992). The derived masses of the warm ISM range from ∼10 3 to ∼10 6 M (Phillips et al 1986;Trinchieri & di Serego Alighieri 1991;Macchetto et al 1996;Goudfrooij et al 1994aGoudfrooij et al , 1994bGoudfrooij et al , 1994cGoudfrooij & de Jong 1995), orders of magnitude below the Xray emitting hot ISM and the stellar mass.…”

Section: Introductionmentioning

confidence: 96%

Nearby early-type galaxies with ionized gas

Annibali

Bressan

Rampazzo

et al. 2010

A&A

122

162

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Aims. A significant fraction of early-type galaxies (ETGs) exhibit emission lines in their optical spectra. We attempt to identify the producing the emission mechanism and the ionized gas in ETGs, and its connection with the host galaxy evolution. Methods. We analyzed intermediate-resolution optical spectra of 65 ETGs, mostly located in low density environments and exhibiting spectros-copic diagnostic lines of ISM from which we had previously derived stellar population properties. To extract the emission lines from the galaxy spectra, we developed a new fitting procedure that accurately subtracts the underlying stellar continuum, and accounts for the uncertainties caused by the age-metallicity degeneracy. Results. Optical emission lines are detected in 89% of the sample. The incidence and strength of emission correlate with neither the E/S0 classification, nor the fast/slow rotator classification. By means of the classical [OIII]/Hβ versus [NII]/Hα diagnostic diagram, the nuclear galaxy activity is classified such that 72% of the galaxies with emission are LINERs, 9% are Seyferts, 12% are composite/transition objects, and 7% are non-classified. Seyferts have young luminostiy-weighted ages ( 5 Gyr), and appear, on average, significantly younger than LINERs and composites. Excluding the Seyferts from our sample, we find that the spread in the ([OIII], Hα, or [NII]) emission strength increases with the galaxy central velocity dispersion σ c . Furthermore, the [NII]/Hα ratio tends to increase with σ c . The [NII]/Hα ratio decreases with increasing galactocentric distance, indicative of either a decrease in the nebular metallicity, or a progressive "softening" of the ionizing spectrum. The average nebular oxygen abundance is slightly less than solar, and a comparison with the results obtained in Paper III from Lick indices shows that it is ≈0.2 dex lower than that of stars. Conclusions. The nuclear (r < r e /16) emission can be attributed to photoionization by PAGB stars alone only for ≈22% of the LINER/composite sample. On the other hand, we cannot exclude an important role of PAGB star photoionization at larger radii. For the major fraction of the sample, the nuclear emission is consistent with excitation caused by either a low-accretion rate AGN or fast shocks (200-500 km s −1 ) in a relatively gas poor environment (n 100 cm −3 ), or both. The derived [SII]6717/6731 ratios are consistent with the low gas densities required by the shock models. The derived nebular metallicities are indicative of either an external origin of the gas, or an overestimate of the oxygen yields by SN models.

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Interstellar matter in early-type galaxies. II - The relationship between gaseous components and galaxy types

Cited by 108 publications

References 0 publications

Cold gas and star formation in a merging galaxy sequence

Cold gas and star formation in a merging galaxy sequence

The gas content of peculiar galaxies: Counterrotators and polar rings

Nearby early-type galaxies with ionized gas

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